Simbody
3.7
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This is an Integrator based on the velocity Verlet algorithm. More...
Public Member Functions | |
VerletIntegrator (const System &sys) | |
Create a VerletIntegrator for integrating a System with variable size steps. More... | |
VerletIntegrator (const System &sys, Real stepSize) | |
Create a VerletIntegrator for integrating a System with fixed size steps. More... | |
Public Member Functions inherited from SimTK::Integrator | |
Integrator () | |
~Integrator () | |
const char * | getMethodName () const |
Get the name of this integration method. More... | |
int | getMethodMinOrder () const |
Get the minimum order this Integrator may use. More... | |
int | getMethodMaxOrder () const |
Get the maximum order this Integrator may use. More... | |
bool | methodHasErrorControl () const |
Get whether this Integrator provides error control. More... | |
void | initialize (const State &state) |
Supply the integrator with a starting state. More... | |
void | reinitialize (Stage stage, bool shouldTerminate) |
After an event handler has made a discontinuous change to the Integrator's "advanced state", this method must be called to reinitialize the Integrator. More... | |
const State & | getState () const |
Return a State corresponding to the "current" time at the end of the last call to stepTo() or stepBy(). More... | |
Real | getTime () const |
Get the time of the current State. This is equivalent to calling getState().getTime(). More... | |
bool | isStateInterpolated () const |
Get whether getState() will return an interpolated state or just the same thing as getAdvancedState() does. More... | |
const State & | getAdvancedState () const |
Return the state representing the trajectory point to which the integrator has irreversibly advanced. More... | |
Real | getAdvancedTime () const |
Get the time of the advanced State. This is equivalent to calling getAdvancedState().getTime(). More... | |
State & | updAdvancedState () |
Get a non-const reference to the advanced state. More... | |
Real | getAccuracyInUse () const |
Get the accuracy which is being used for error control. More... | |
Real | getConstraintToleranceInUse () const |
Get the constraint tolerance which is being used for error control. More... | |
SuccessfulStepStatus | stepTo (Real reportTime, Real scheduledEventTime=Infinity) |
Integrate the System until something happens which requires outside processing, and return a status code describing what happened. More... | |
SuccessfulStepStatus | stepBy (Real interval, Real scheduledEventTime=Infinity) |
Integrate the System until something happens which requires outside processing, and return a status code describing what happened. More... | |
Vec2 | getEventWindow () const |
Get the window (tLow, tHigh] within which one or more events have been localized. More... | |
const Array_< EventId > & | getTriggeredEvents () const |
Get the IDs of all events which have been localized within the event window. More... | |
const Array_< Real > & | getEstimatedEventTimes () const |
Get the estimated times of all events which have been localized within the event window. More... | |
const Array_< Event::Trigger > & | getEventTransitionsSeen () const |
Get EventTriggers describing the events which have been localized within the event window. More... | |
bool | isSimulationOver () const |
Get whether the simulation has terminated. More... | |
TerminationReason | getTerminationReason () const |
Get the reason the simulation terminated. More... | |
void | resetAllStatistics () |
Reset all statistics to zero. More... | |
Real | getActualInitialStepSizeTaken () const |
Get the size of the first successful step after the last initialize() call. More... | |
Real | getPreviousStepSizeTaken () const |
Get the size of the most recent successful step. More... | |
Real | getPredictedNextStepSize () const |
Get the step size that will be attempted first on the next call to stepTo() or stepBy(). More... | |
int | getNumStepsAttempted () const |
Get the total number of steps that have been attempted (successfully or unsuccessfully) since the last call to resetAllStatistics(). More... | |
int | getNumStepsTaken () const |
Get the total number of steps that have been successfully taken since the last call to resetAllStatistics(). More... | |
int | getNumRealizations () const |
Get the total number of state realizations that have been performed since the last call to resetAllStatistics(). More... | |
int | getNumQProjections () const |
Get the total number of times a state positions Q have been projected since the last call to resetAllStatistics(). More... | |
int | getNumUProjections () const |
Get the total number of times a state velocities U have been projected since the last call to resetAllStatistics(). More... | |
int | getNumProjections () const |
Get the total number of times a state has been projected (counting both Q and U projections) since the last call to resetAllStatistics(). More... | |
int | getNumErrorTestFailures () const |
Get the number of attempted steps that have failed due to the error being unacceptably high since the last call to resetAllStatistics(). More... | |
int | getNumConvergenceTestFailures () const |
Get the number of attempted steps that failed due to non-convergence of internal step iterations. More... | |
int | getNumRealizationFailures () const |
Get the number of attempted steps that have failed due to an error when realizing the state since the last call to resetAllStatistics(). More... | |
int | getNumQProjectionFailures () const |
Get the number of attempted steps that have failed due to an error when projecting the state positions (Q) since the last call to resetAllStatistics(). More... | |
int | getNumUProjectionFailures () const |
Get the number of attempted steps that have failed due to an error when projecting the state velocities (U) since the last call to resetAllStatistics(). More... | |
int | getNumProjectionFailures () const |
Get the number of attempted steps that have failed due to an error when projecting the state (either a Q- or U-projection) since the last call to resetAllStatistics(). More... | |
int | getNumConvergentIterations () const |
For iterative methods, get the number of internal step iterations in steps that led to convergence (not necessarily successful steps). More... | |
int | getNumDivergentIterations () const |
For iterative methods, get the number of internal step iterations in steps that did not lead to convergence. More... | |
int | getNumIterations () const |
For iterative methods, this is the total number of internal step iterations taken regardless of whether those iterations led to convergence or to successful steps. More... | |
void | setFinalTime (Real tFinal) |
Set the time at which the simulation should end. More... | |
void | setInitialStepSize (Real hinit) |
Set the initial step size that should be attempted. More... | |
void | setMinimumStepSize (Real hmin) |
Set the minimum step size that should ever be used. More... | |
void | setMaximumStepSize (Real hmax) |
Set the maximum step size that should ever be used. More... | |
void | setFixedStepSize (Real stepSize) |
Set the integrator to use a single fixed step size for all steps. More... | |
void | setAccuracy (Real accuracy) |
Set the overall accuracy that should be used for integration. More... | |
void | setConstraintTolerance (Real consTol) |
Set the tolerance within which constraints must be satisfied. More... | |
void | setUseInfinityNorm (bool useInfinityNorm) |
(Advanced) Use infinity norm (maximum absolute value) instead of default RMS norm to evaluate whether accuracy has been achieved for states and for constraint tolerance. More... | |
bool | isInfinityNormInUse () const |
(Advanced) Are we currently using the infinity norm? More... | |
void | setInternalStepLimit (int nSteps) |
Set the maximum number of steps that may be taken within a single call to stepTo() or stepBy(). More... | |
void | setReturnEveryInternalStep (bool shouldReturn) |
Set whether the Integrator should return from stepTo() or stepBy() after every internal step, even if no event has occurred and the report time has not been reached. More... | |
void | setProjectEveryStep (bool forceProject) |
Set whether the system should be projected back to the constraint manifold after every step. More... | |
void | setAllowInterpolation (bool shouldInterpolate) |
Set whether the Integrator is permitted to return interpolated states for reporting purposes which may be less accurate than the "real" states that form the trajectory. More... | |
void | setProjectInterpolatedStates (bool shouldProject) |
Set whether interpolated states should be projected back to the constraint manifold after interpolation is performed. More... | |
void | setForceFullNewton (bool forceFullNewton) |
(Advanced) Constraint projection may use an out-of-date iteration matrix for efficiency. More... | |
Additional Inherited Members | |
Public Types inherited from SimTK::Integrator | |
enum | SuccessfulStepStatus { ReachedReportTime =1, ReachedEventTrigger =2, ReachedScheduledEvent =3, TimeHasAdvanced =4, ReachedStepLimit =5, EndOfSimulation =6, StartOfContinuousInterval =7, InvalidSuccessfulStepStatus = -1 } |
When a step is successful, it will return an indication of what caused it to stop where it did. More... | |
enum | TerminationReason { ReachedFinalTime = 1, AnUnrecoverableErrorOccurred = 2, EventHandlerRequestedTermination = 3, InvalidTerminationReason = -1 } |
Once the simulation has ended, getTerminationReason() may be called to find out what caused it to end. More... | |
Static Public Member Functions inherited from SimTK::Integrator | |
static String | getSuccessfulStepStatusString (SuccessfulStepStatus) |
Get a human readable description of the reason a step returned. More... | |
static String | getTerminationReasonString (TerminationReason) |
Get a human readable description of the termination reason. More... | |
static String | successfulStepStatusString (SuccessfulStepStatus stat) |
OBSOLETE: use getSuccessfulStepStatusString(). More... | |
Protected Member Functions inherited from SimTK::Integrator | |
const IntegratorRep & | getRep () const |
IntegratorRep & | updRep () |
Protected Attributes inherited from SimTK::Integrator | |
IntegratorRep * | rep |
This is an Integrator based on the velocity Verlet algorithm.
It is a third order, semi-explicit integrator. Velocity independent forces only need to be evaluated once per time step, but forces which depend on velocity must be evaluated multiple times. This makes it a very efficient algorithm for systems where most of the time is spent evaluating forces that depend only on position.
Although this is a third order integrator, the velocities reported at each time step are only accurate to lower order. If any forces depend on velocity, this may lead to a reduction in the overall accuracy of integration, since the forces being integrated are less accurate than the method used to integrate them. Whether this actually happens in a particular case depends on the magnitude of the velocity dependent forces, how sensitive they are to errors in velocity, and how the system is affected by those forces.
When this integrator is used with fixed size time steps, it is symplectic. This means that it is extremely good at conserving energy, and will usually produce much less variation in energy than most other integrators would at the same step size. This makes it a good choice for problems where accurate energy conservation over long time periods is important. To use it in this way, use the constructor which takes a step size, or call setFixedStepSize().
Alternatively, it may be used in variable step mode, in which case the step size is selected based on the accuracy specified by calling setAccuracy(). In this case it is no longer symplectic, so the energy will fluctuate more over time. Because the step size is adjusted based on the local error in each step, however, the trajectory will generally be more accurate in variable step size mode than would be obtained with the same number of fixed size steps spanning the same amount of time.
Another possible strategy is to set only a maximum step size but not a minimum step size. It should be chosen such that most time steps will use the fixed maximum step size, but smaller steps can be used when necessary to preserve accuracy. This leads to fairly good long term energy conservation, while still maintaining reasonable accuracy when unusually large forces transiently occur.
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explicit |
Create a VerletIntegrator for integrating a System with variable size steps.
Create a VerletIntegrator for integrating a System with fixed size steps.